[Motorola] Research Line for amateur use

[Geoff Fors]

Regarding Tom's questions, the Twin-V was a vibrator powered unit. The use
of the transistor did not occur in trunk mount mobiles until the T-Power
sets were marketed in 1958.  Interestingly, Motorola made a conversion kit
sometime in the 1960's to be retrofitted to the even-then-ancient
FMTRU-140(D) dynamotor powered radios, which made them transistor powered.
The dynamotor was discarded and a big heatsink was bolted to the front.
Those models then had the (D) on the model # nameplate overstruck with a "T"
so that the new model became FMTRU-140(T).  I presume the kit only worked
for 12 volt equipment, so possibly the kit also converted a 6 volt radio to
12.  GE had the same sort of kit for the Progress Line mobiles, and
presumably RCA did for its "Carfone" series sets.

By the way, the first largely transistorized equipment made by Motorola was
the Industrial Dispatcher, a compact motorcycle / forklift radio which was
also repackaged into a pack-set "Handie Talkie" unit of lower power with a
chrome handle across the top and two-tone paint job.  Those started out with
hybrid receivers and almost all tubes in the transmitter (except the mike
amp.)  They were introduced slightly ahead of the T-Power mobiles, due to
the high demand for a low-battery-drain motorcycle radio.  The last
Industrial Dispatchers had fully solid state receivers, although the
transmitters remained the same throughout the production run.  The
transmitters were full of 1AD4 wire lead submini tubes, with several 6397's
as drivers feeding a 2E24 "instant heating"  final.

The UHF Motrac, as all Motracs actually, have tube finals.  The Motran is
the one which is all solid state, although I vaguely recollect there may
have been just one high power UHF version with a tube in the PA.   The
confusion seems to come from the fact that the few tubes the most modern
Motracs used were hidden inside the rear heat sink, with the exciter being
fully solid state.

Concerning Research Line gear, you might be surprised that there are still a
number of ham repeaters using the Sensicon "A" receiver strips because of
their immunity to high RF fields and superior IMD performance, due in part
to the nice cavity "pipes" in the front end.  The tubes last a long time and
all you have to worry about is the electric bill. I used to use type 5654
surplus radar tubes in the front end instead of the 6AK5's, and you could
expect about 0.4 microvolt sensitivity out of one of them on VHF.  The
lowband sets were pretty sensitive, down there about 0.3 microvolt.


Geoff Fors